Catalyst and method



CATALYST AND METHOD Eduard Farber, Washington, D. 'C.,;assig nor-to Timber- Engineering Company, Washington, D. C., a corporation of Delaware No Drawing. Application November.18, -1952,

Serial No. 321,290

4 Claims. (Cl. 260-71).

' Thisinvention relates to maleic' acid-containing catalysts useful to effect the setting of adhesives comprising urea-formaldehyde resins; to processes entailing the utilization of such catalysts in the production of laminated wood products, the' plies .of which are 'b'onded together with urea-formaldehyde resin adhesives; and to thelaniinated wood products thereby obtained.

It is known that intermediatecondensates of urea and formaldehyde are convertible' into the"final-" stages 'of resinification by catalysts of acidfuuction'." Efforts of the art to capitalize on this property of theuremforma'ld'ehyde resins, through utilization thereofsas cold-setting glues in the production of laminated wood structures, have been fraught with problems forwhich no satisfactory solution was heretofore known.

Many factors mitigate against the successful utilization of acid catalyzed urea-formaldehyde resin adhesives in p the manufacture of wood laminates. A particularly acute problem resides in the provision of a physiologically innocuous catalyst capable of setting or converting such urea-formaldehyde resin glues with a rapidly requisite to commercial utilization thereof which does not attack and materially Weaken the wood structure. 1 It is essential to the commercial production of wood laminates-that'the urea-formaldehyde resin adhesiveju'tilized set to a degree such that the laminated structure can be removed from the clamps or presses after a relatively short clamping or pressingperiod. In general up to about minutes of clamping or pressing time may be tolerated incommercialoperation. H H V -It has been theexperience of the art that to achieve the desired rate"of cold-setting of ureaeformaldehyde resin a es e nly ron m e al id. such, hyd ochloric acid; sulfuric acid, nitric acid andthe ;like,f and. organic acids in unduly. high'concentratiomJma be emd Strong mine'ralacidsfareunsuitable for?the""prodl Gt cjin'' of woodla'mina'tes fortliereason that such acids weaken the wood structure surrounding" the resin-wood bond,

Furthermore, such mineralacids; over a period of time, tend-=to-impart increasing brittleness to the resinbond' p'er-se and 1 hence shorten unduly. the "satisfactory per od ofqperformance' of the l'aminated'structure.

;;Many-organic acids, in high concentration,slikewise" attack and weaken :the wood structureor have otherwise proved unsatisfactory j in the-.-art.--- For exampleformic acid, when present in effective concentration, is 'objec-;

tionable by virtue of the high degree of vaporization resulting therefrom, and the consequent unfavorable physiological effects of the vapor produced. Many non-volatile organic acids present solubility problems andu-the like, which render the utilization thereof impractical as catalysts for urea-formaldehyde resin'adhesive's to'be utilized t in: wood laminatingoperations; 'Catalyst'compositioris to about 40% by weight ofm'aleic acid."

embracing organic acids in high concentration havefur-' ther: presented problems relative to the spreadability of thecatalyst'or' adhesive composition, the extendability of such compositions with-water and conventionalsolid fillers and the like,"which* have not ibeensolved by the prior art;

*It is 'a primary object'of this invention to" provide a commercially practical method of formulating wood laminatesientailing the utilization of cold-settingsurea formaldehyde resin'adhesiv'esa "i i x: It'isa further primary' and salient objectof'ithis'invention to"provide* aicatalyst, :havi'ng no' ma'terial adverse effect on the wood 'structure', th'rough the utilization of which urea-formaldehyde" resin *adhes'ives mayv be 'set' within a time requisite 'to" the commercial Q utilization thereof.injthe'pro'duction of Woodl'aminates. 7

"Applicant has discovered that the function of a catalyst in effecting the setting or conversion of urea-formaldehyde resinadhesivesis not dependent solely upon the'relative strength as an acid of the catalyst utilized, but alsoup'on the structure of the organic acid molecule employed as theicatalystr i I In accordance with l the present invention, it uhas' been discovered' that wood laminates maycommercially be produced through the utilization of cold-setting ureaformaldehydeadhesives,'there being employed to catalyze the setting 'of' such resin-adhesives an aqueous solution containing from about 10% to about'20% by weight ofmale'ic acid. I 'Itwill-be appreciated 'by those 'skilled in the artthat' fromaneconomic standpoint it mightibe undesirable to'ship catalyst solutions containingtherelativelysmall amounts of maleic acidwhich are requisite'to the practice" of this invention; 'To obviate the economic problem stemmingafrom the'presence ofla'rg'e quantities of water 'in the compositionsof' this invention, it is contemplated to 5 provide catalyst concentrates whiclrmay be diluted [byf theultimate' userrto the appropriate maleicacid concen trationi such'imaleic' acid concentrates may desirably embrace aqueous "solutions containing-from about 20% In'-Table l-arei-recorded' comparative data illustrative of the unusual and unexpected'properties of'maleic acid to effect conversion .of. urea-formaldehyde resin adhesives through the final-stage of' resinification. 1 The data =.appearing in Table I-were-obtained by dispersing'S grams of intermediate stage urea-formaldehyde resin in" 2 grams of water andthereafter incorporating, with agitation, theacid catalysts listed,-.in the concentrationsindicated. -In each instance vthe agitation was continued so long as per-- mined by the' increasingviscosity of the mixture. The urea-formaldehyde resin utilizedwas the. product" of, the reactionofurea' andtformaldehyde in a mole ratio of about 11-1 to about 1 :2 ata temp erature of about 150? R, forabout minutes,. in the presence of acatalyst; It:

was a commercial :product sold :by theiRohm 'andvI-Iaasl Company, under the trade name of Urea Resin 500.

TABLE 1 [Convcrsion of intermediate urea-formaldehyde resin glue by catalysts added to 5 grams of glue in 2 grams of water] Catalyst Time in Seconds for- Concen- Milli- Mllli- M1111- tration, Start of Soft Hard Name of Acld percent ggg 32 3 %g; gelation set set used Maleic 7. 6 76 0. 66 1. 32 120 D 11. 115 l. 0 2. 0 50 23 230 2. 0 4. 0 25 20 200 2. 6 2. 6 600 50 500 6. 6 6. 6 300 5 100 1. 1 l. 1 l, 500 10 200 2. 2 2. 2 600 500 5. g 5 240 20 200 2. 2

4 20 0. 11 34 180 20 200 1. 5 3. 0 570 40 400 3. 0 6. 0 100 10 100 O. 66 1. 98 780 10 200 l. 3 3. 9 300 10 240 1. (i 4. 8 180 20 200 l. 0 3. 0 500 12 240 1 No action after 20 hours.

It will be observed from Table I that maleic acid in dilute aqueous solution is characterized by the unusual and unexpected property of effecting extremely rapid setting of urea-formaldehyde resin adhesives. No one of the other acids listed in Table I is comparable in effect to maleic acid, even though utilized in concentrations requisite to provide a hydrogen ion concentration many TABLE II Conditioning Time One Week Conditioning Time One Month gg gl ii than that provlded by the 131616 acld Ultimate Shear Stress, gggg Ultimate Shear Stress, The unusual effectiveness of maleic acid in converting r nt Percent urea-formaldehyde resin adhesives is of major significance in the art of Wood lamination. In general, through ,1 3 ,12 34 the practice of this invention, laminated wood structures i bonded with urea-formaldehyde resins may be removed from the clamps after only about 10 minutes. Clamping for about 10 to about 30 minutes 'is preferred. In consequence thereof, cold-setting urea-formaldehyde resin glues may practically be employed in the commercial production'of laminated wood structures. By virtue of the extremely rapid rate of setting, the time required to effect initial setting of the .adhesive to a degree requisite that the laminated structure may be removed from the clamps, is materially reduced and the total output of the laminating 'plant thereby increased.

It is the hypothesis of applicant, that the unusual and TABLE III specificproperties of maleic acid as a catalyst to effect the setting or conversion of urea-formaldehyde resin adhesizes, are attilibutatlfle. in laige measlure to the unsaturation Condmonmg Stress, Failure,

in erentin t ema eic aci m0 ecu e. ps- 1 P rc nt Wood laminates formulated in accordance with the method of this invention demonstrate no objectionable Western white pine:

degree of weakening or degradation of the wood struc- 1 Week ture. The maleic acid utilized as a catalyst has no mate- $08 9 rial adverse effect upon the strength of the ultimate lami- 1,647

nated product produced, even after long periods of time. 48 In Table II are recorded data obtained by subjecting White 43 to shear tests, carried out in conformance with ASTM lweek' H 1,664 31 specification D9050-49 entitled Test for Strength Prop- 1 month 1.800 33 erties of Adhesives in Shear by Compression Loading,

hard maple blocks glued together in accordance with the method of this invention. The samples tested were obltls apparent f fi data recorded Tables P- tained by gluing together hard maple blocks having the 70 III that the maleic acid catalyst compositions of this 1ndirnensions of X 2 /2" x 12". The so-glued blocks were then cut to conform to the dimensions of 2 x 2" x Samples having these latter dimensions were utilized in carrying out the test. The blocks were glued together by applying to one of the surfaces to be joined a urea-formaldehyde resin adhesive of the type described with reference to Table I, in about 66% concentration by weight, as an aqueous dispersion, and applying to the other surface to be joined an aqueous solution of maleic acid containing about 15% by weight of maleic acid, and thereafter joining the two so-coated surfaces and maintaining the'joined surfaces in clamps under a pressure of about 100 to 250 lbs. per square inch for a'period of about 10 minutes at a temperature of about 70 F. The data recorded in Table II are average data, resulting from vention do not adversely weaken or degrade the wood structure of the wood plies, laminated'in accordance with the invention, to any material extent.

It is critical to this invention that the maleic acid be utilized in aqueous solution in a concentration of from about 10% to about 20% by Weight. If the lower-limit of 10% by weight is not observed, the concentration of maleic acid is ineffective to effect conversion of the urea-formaldehyde resin adhesives in a time requisite to commercial utilization thereof in'the productionof wood laminates. If theconcentration of the maleic acid materially exceeds the upper limit of about 20% by weight in the catalyst solution, the aciditythereof may be such as to adversely affect the quality of the laminated wood product.

.400 to, about-4,000 'centipoisesL In the catalyst Iconcentrates of this invention, methyl cellulose may desirably be present in an amount equal to from about 0.4%. to about.2%of the weight thereof. x r I It has been discoveredthatthe presence f methyl cellulose in ithejcatalyst composition renders s, the*'composition useful for all species of wood whichsit may be desired to laminate. Wood surfaces vary greatly. in permeability andsurfac'e texture. Unmodifiedaqueous solutions of maleic acid may, in many instances, penetrate too rapidly into certainglspecies of wood or types of wood surface with the. result ith'atgan unsatisfactory bond is obtained. Exemplarylof woodswhich'may'be penetrated with-undue rapidityaresouthern yellow. pine;

basswood, and certain oaks. Throughtheiutilization of methyl cellulose in conjunctionwith the maleic acid catalyst, it has been discovered that: this invention t-may be practiced to effect the laminationof all woods.

Furthermore, the presence of. methyl cellulose 'in.the

catalyst composition renders feasible the. incorporation thereinto of Wood flour, clay,; and like solid fillers con-' ventionally employed in the-art., Also, the presence of the methyl cellulose in thercatalyst composition. of the present invention'tends to increasethe assembly-line tolerance of thecatalystcomposition whereby'the' tendency.

of the catalyst to -migrate. from-theglue. lineor otherwise to be affected inhsuch a" manner asto prevent the" formation of a strong glue bond is obviated; 'It. is critical, however, that the methyl cellulose be present in the catalyst-composition of this invention within' theaforementioned limits of concentration and viscosity.

The ureaformaldehyde resin-adhesives;as*a class, ar

suitable for the purposes ofithe present invention Preferred are those resinous products 'resultingafromgthe reaction of urea and formaldehyde in aLmQl'e ratio of from about 1:1 to about 1:2, inthe presence of a cata lyst, until the reaction product*has reached an inter-i mediatestate of condensation such'that upondilution of tion thereto of the methyl'cellulose." In apreferrefd em bodiment,; maleic anhydride is first dissolved in water having a temperature of about 100 F. toab'out 180 F}, to; form a solution containing about 40% to about 60% by weight of maleic acid;- Thisconcentrated solution is p then diluted to form a solution containing about 30% to about 40% by weight ofmaleic acid,-whicl1 may be shipped as'a catalyst concentrate,andv ultimately diluted to produce a finalcatalystcomposition containing maleic acid inthe above-defined criticalrange of about 10% to abou.t"20%. by weighQ Met hyl cellulose may .be, added to {either the catalyst concentrate or to the finalcatal'yst composition. If the methyl cellulose is added to the catalyst concentrate, it"is appropriately incorporated in an amount such that the compositioncontains from about 0.4%:to about 2% of methyl cellulose The finalcataly st composition, in' any'event, should contain from about 0.2% to' about 2.0% 'ofmethyl cellulose "as hereinbefore specified.

The methyl cellulose dispersion utilized may suitably be prepared by stirring commercial methyl cellulose in warm water having a temperature of about 140 F. to about 160 F. to form a mixture containing from about 5 to about 15% by weight of methyl cellulose, permitting the mixture so formed to swell for a few hours, preferably about 2 to 6 hours, and thereafter diluting the prodnot so obtained. It is not essential that the methyl cellulose be completely dissolved before incorporation into the maleic acid Solution,

Commercially, the present invention may be utilized by the application to one of the wood'surfaces to be bonded of a urea-formaldehyde resin adhesive composition containing no catalyst, and the application to the opposing surface to be bonded of a maleic acid catalyst composition of the type described herein. The so-coated surfaces are thereafter placed in. contact andfclampedat room temperature, i. e., a temperature of from about 60 F. to about 80 F., for; a period of from about 10 to about 30 minutes. In the course. of this clamping operation the adhesive forms a bond of requisite strength to permit removal of the laminated product from the press: The bond becomes stronger and'cures with the passage of time. a

The followingexamples are illustrative'of the practice of this invention: t Q

This example is illustrative ofthejbestmodeknownto applicant for the preparationof the catalyst compositions of this invention. 104 lbs; ofmaleic' anhydride are placed in a .50 gallon containe'nland approximately 8 gallons of water, at a'temperature'ofapproXimately 108 R, are added rapidly to the'maleic"anhydridefin the container, and the mixture stirred, with'a wooden paddle until all of the solids are dissolved. Cold water is then added in an amount sufiicient to produce an ultimate solution containing about 20%rby weight of maleic acid. The ultimate strengthof the maleic acid catalyst solution so obtained may, of course, be varied by varying, the amount of cold water added to thehot aqueous solution produced. Y 9

7 Example 2 This example is illustrative of the preparation of a catalyst composition of this invention containing methyl cellulose.

"104 'lbs. of'maleic anhydride are placed in a"50 gal lon container. afitemperature of about 108 'F;, are added rapidly. to the maleic anhydride, and the mixture stirred "fora time requisite to effect solution of all of the solidspresent. Cold water is then added, with agitation, inan amount requisite to form an ultimate'solution having a total weight of 300 lbs. g

About 4 lbs of methyl cellulose, in about 8' gallons of water are then added, with agitatiomi tol the maleic acid solution previously formed, the product thereby obtained diluted with cold water until the total weight thereof is'800 lbs. The methyl cellulose utilized was characterizedjbya viscosity in 2% aqueous solution'at 20C. of about 1,500 centipoises, specific viscosity;

-The;,methyl' cellulose dispersion utilized was pre-. pared by stirringpS-lbs. of the methyl cellulose into about 10 gallons of water at {a temperature of about F. The mixture so formed, was permitted to swell for "a few hours and then diluted to an ultimate' volumof.

20' gallons; such that 2" gallons of theidispersion'. con- Blocks .ofzhard maple, western white pine", red gum, and white. oak; having the dimensions 2' /2' 1 2" were utilized The blocks were bonded "together with urea-formaldehyde resin adhesives set by the catalysts of this invention. In each case, one surface of the surfaces to be joined was coated with an aqueous dispersion containing about 66% by weight of a ureaformaldehyde resin adhesive, and the other of the surfaces to be joined was coated with a catalyst composition of the type embraced by this invention, containing maleic acid in the proportions indicated in Table IV. The so-coated surfaces are thereafter placed in clamps under pressure of about 250 lbs., at a temperature of about 70 F., for a period of 10 minutes. The so-bonded blocks were tested immediately in a Baldwin-Southwark testing apparatus of the type described with reference to Table II. The urea-formaldehyde resin adhesive employed was of the same type as that described in Table I. The data recorded in Approximately 8 gallons of-waten at in 'the art,

7 Table-JV are average results obtained::by testingfive such bonded blocks.

TABLE IV lgreeyn: by nsvlerage Aviaerage mg eer 00 "species Maleic Stress, 1 Failure,

Acid p. s.;i. 1 Percent Hard maple 10 379 0 Do 13 487 0 0 15 541 0 Western white pine 10 228 0 D0. 10 229 0 Do. 13 281 0 D0. l5 5 361 1 0 e 0; 2. 0 D0,. 121 0 Do. 13 314 0 Whiteoak. 10 261 0 'Do. 510 273 0 D0,. 13\ 30 41 '0 D0 15 474 0 D0 -20 520 10 Example 4 The series of tests described, in Example. 3' were repeated with the exception that in this instance the tests were delayed until seven days subsequent to the initial gluing operation.

From a comparison of Tables IV and V, it is-apparent that the strength of the bond formed by the methods of this invention increases rapidly with the passage of time, .and that the catalyst utilized does not ad versely affect the strength of the wood ad acent the glue line. It :is further evident from an examination of Table IV that the glue bond between the blocks 15 of sufiicient strength after 10 minutes clamping to permit removal of the laminated product from the clamps and handling or storage-thereof.

Example 5 The method of this invention is not restricted to the lamination of wood laminae, but may be utilized with equal effectiveness to bond plastic materials, glass, and the like, to wood. For example, the method described in Examples 3 and 4 may be utilized to bond plastic materials such as melamine formaldehyde resins, polystyrene, glass, and the like, to wood. In a particular embodiment, a sheet of melamine formaldehyde resin was coated with a catalyst composition-containing about 15% of ma'leic acid'and'about 0.5% of methyl cellulose in Water anda surface of a Douglas fir block having' the dimensions of 2 /2"'- 12 was coated with an aqueous dispersion of a urea-formaldehyde resin adhesive-of the type-described-in Example 3. The laminate so formed was placed in clamps under a pressure of about 40 lbs. per square inch at a temperature of about F. for a period of about 20 minutes. A satisfactory laminate was produced.

:When the process of this invention ;.is utilized to bond resinous materials to wood, the laminates are preferably subjected to a pressure of about 20 to about lbs. per square inch in the bonding operation.

Iclaim:

1. A catalyst for cold-setting urea-formaldehyde resinadhesives consisting essentially of an aqueous solution containing from about 10% to about 20% by weight .of maleic acid, there being present in said solution-methyl cellulose in an amount equal to from about 0.2% to-about 2.0% :of the weight thereof.

2..A catalyst concentrate consisting essentially of an aqueous solution containing from about 20% to about 40% by weight of maleic acid, there being present in said solution methyl cellulose-in an amount equal to from about 0.4% to-about 2% by weight thereof.

3. The method of preparing a catalyst for cold-setting vurea-formaldehyde resin adhesives which consists essentially ofdissolving maleic anhydride in water maintained at'a [temperature of from about 100 F. to about 180 F. in an amount requisite to form a first solution containing from about 40% to about 60% by weight of. maleic acid; thereafter diluting said solution to form a second solution containing from about 10% to about 40% by- Weight of maleic acid, and thereafter incorporating .into said second solution a mixture of methyl celluloseand water, said mixture containing from about 5% -to..about 15% by weight of methyl cellulose and being prepared by stirring methyl cellulose into water maintained at a temperature .-of from about F. to about P. and thereafter permitting the composition so formed to stand for a period of about 2 to 6 hours, theamount of said mixture added to said second :solution being such that the ultimate composition produced contains from about 0.2% to about 2% by weightofmethyl.cellulose.

4. The process which comprises converting, at room temperature in a time period of not more than about 10 to 30 minutes, a urea-formaldehyde resin adhesive to a solid, strongly coherent body, by applying as a cold setting catalyst to said adhesive an aqueous solu tion containing from 7.6% to about 20% by weight of maleic acid, said catalyst being employed in an amount sufiicient. to provide at least about 1.5 parts of maleic-acid for each 100 parts by weight of ureaformaldehyde resin in said adhesive.

References Cited in-the'file of this patent UNITED STATES PATENTS Number Name Date ll; 922,690 Liougovoy Aug. 15, 1933 2,453,608 West Nov. 9, 1948 FOREIGN PATENTS Number Country Date 281,717 Great Britain Apr. 5, 1929 435,041 Great Britain Sept. 12, 1935 

4. THE PROCESS WHICH COMPRISES CONVERTING, AT ROOM TEMPERATURE IN A TIME PERIOD OF NOT MORE THAN ABOUT 10 TO 30 MINUTES, A UREA-FORMALDEHYDE RESIN ADHERSIVE TO A SOLID, STRONGLY COHERENT BODY, BY APPLYING AS A COLD SETTING CATALYST TO SAID ADHESIVE AN AQUEOUS SOLUTION CONTAINING FROM 7.6% TO ABOUT 20% BY WEIGHT OF MALEIC ACID, SAID CATALYST BEING EMPLOYED IN AN AMOUNT SUFFICIENT TO PROVIDE AT LEAST ABOUT 1.5 PARTS OF MALEIC ACID FOR EACH 100 PARTS BY WEIGHT OF UREAFORMALDEHYDE RESIN IN SAID ADHESIVE. 